1. Field of the Invention
The present invention relates to a process for setting a uniform characteristic cross-direction profile for a paper web with regard to at least formation, basis weight, and fiber orientation in a paper machine via a headbox, in which consistency is sectionally adjusted and which has an adjustable die exit opening.
2. Discussion of Background Information
The Voith Sulzer publications "Module Jets.RTM.: the New Headbox for Independent Control of Cd Basis Weight and Fiber Orientation Profiles," p2919e, (March 1994); "Module Jet--erste Betriebserfahrungen mit dem neuen Stoffauflaufkonzept," Wochenblatt fur Papierfabrikation 122, No. 12, pages 485-491 (1994), and "Stoffdichteabhangige Querprofilregelung--Betriebserfahrungen," Das Papier, volume 49, issue 10A, pages V99-V105 (1995) disclose the state of the art with regard to the process generally discussed above, and the disclosures of these documents are expressly incorporated by reference herein in their entireties.
From the above-noted publications, it is known to locally adjust the amount of solid matter deposited by an appropriate mixing of pulp slurry and a dilution liquid, eg., backwater, to reduce basis weight irregularities in a consistency-regulated headbox. It is further disclosed that the cross flow can be adjusted, and, therefore, the fiber cross-direction profile can be improved, by adjusting the sectional flow rate of pulp slurry at the die exit opening. These documents seek to achieve as even a flow across or over the screen at the die exit opening as possible. Moreover, it is assumed that there is a connection or relationship between the specific pulp slurry flow rate (measured in liters per meter of machine width) deposited at the headbox and the formation cross-direction profile, especially in twin wire formers.
Therefore, in the state of the art, problems arise in providing a process for operating a headbox, which maintains the known good quality of the basis weight cross-direction profile and the fiber orientation cross-direction profile that can be achieved by a consistency-regulated headbox and simultaneously has a positive influence on the fiber orientation cross-direction profile.